Roaming is the ability to obtain wireless telephone service using a cellular mobile radiotelephone (CMR) that is located outside the area served by the CMR's home wireless telephone service provider. A large number of wireless telephone service providers have entered into contractual arrangements that allow CMRs associated with accounts in good standing to obtain roaming service throughout most of the United States, Canada and other areas in the North American Number Plan (NANP). The NANP specifies a format for telephone numbers that consists of an number plan area (NPA or area code), a 3 digit central office code, and 4-digit line number. This is frequently depicted as "NPA-NXX-XXXX." The subscriber who is responsible for the CMR's account receives a unified bill from his or her home wireless telephone service provider that includes charges for home as well as roaming service. Once the bill is paid, the CMR's home wireless telephone service provider forwards appropriate proceeds to the other carriers that provided the CMR with roaming service.
Local number portability (LNP) is the ability to retain the same directory number while changing service providers. Without LNP, changing a CMR's wireless telephone service provider requires changing the directory number. Changing a CMR's directory number can be inconvenient and expensive, particular for businesses that may have to contact their customers, run new advertisements, print new stationary, and so forth, as a result of obtaining a new directory number. Many subscribers might therefore be reticent to change their home wireless telephone service provider if doing so meant that they also had to change their CMR's directory number. For this reason, it is generally recognized that LNP would enhance competition in the provision of wireless telephone service.
The mobile directory number (MDN) assigned to a CMR is presently used as a mobile identification number (MIN) that uniquely identifies the CMR to the service provider. The first six digits of the CMR's MIN/mobile directory number (the NPA-NXX portion) uniquely identifies the CMR's home MSC. Other MSCs use the NPA-NXX to route telephone calls through the public switched telephone number to the CMR's home MSC. In addition, a host MSC receiving a registration request from a roaming CMR uses the CMR's MIN to validate the CMR for roaming service. The host MSC validates the CMR by sending a registration notification message to the operator of the CMR's HLR, which is typically located at the CMR's home MSC or a clearinghouse. This is accomplished by using, in part, the Signaling System 7 protocol and procedures. If the account associated with the CMR is in good standing, the operator of the CMR's HLR returns a validation response message to the host MSC. In response, the host MSC registers the CMR for roaming service.
MSCs across the United States and Canada are presently configured to default to using a CMR's MIN as the mobile directory numbers. This is then frequently used for billing and supplementary services, such as calling line ID, which require use of the originating MDN. These purposes rely on the MIN being the same as the CMR's directory number. That is, MSCs across the United States and Canada are presently configured to use a CMR's MIN/directory number to uniquely identify the CMR's home MSC when routing telephone calls to the CMR, to identify the location of the CMR's HLR when registering the CMR for roaming service, and for billing and calling line ID purposes. As a result, a CMR's MIN cannot presently be changed to a number other than the CMR's directory number without disrupting roaming service or reconfiguring virtually all of the MSCs across the United States and Canada to handle MINs that are distinct from the corresponding CMR's directory number.
Once LNP is implemented, however, a subscriber may change their service provider changing the CMR's directory number. For this reason, the first six digits of the CMR's directory number (the NPA-NXX) will no longer uniquely identify the CMR's home MSC. In designing the architecture for Wireless LNP, the industry has proposed separating the MIN from the mobile directory number (MDN). Specifically, the MIN is no longer the same value as the MDN. In a fully LNP-enabled telecommunications system, each CMR will be assigned a MIN and a separate MDN. The MW will by used for paging a mobile station and roaming registration purposes and, thus, will identify the corresponding CMR's home MSC. As such, the CMR's MIN will change whenever the CMR's home MSC or service provider changes. The MDN, on the other hand, will remain the same when the CMR's home MSC changes and is used for routing of calls and identifying the originator of a call.
Reconfiguring an MSC to support CMRs with separate MINs and MDNs is also referred to as making the MSCs LNP enabled or supporting MIN/MDN separation. Separating MINs and MDNs would not disrupt roaming service if all of the MSCs that act upon the MIN could be simultaneously updated to make them LNP enabled. But this is unlikely to occur because the Federal Communications Commission has initially ordered LNP implementation in only the largest 100 metropolitan service areas. Moreover, it is not known if or when Canada and other areas in the North American Number Plan Area will implement LNP. It therefore appears that LNP may be partially implemented in the United States and Canada for the foreseeable future.
Partially implementing LNP could interfere with the provision of roaming service to ported subscribers in those areas that are not LNP enabled. For example, if a host MSC uses the CMR's MIN rather than its MDN as the originating directory number, interexchange carriers may use the MIN value for billing purposes, potentially resulting in incorrect billing of toll calls. Moreover, the calling line ID feature, which may be used by emergency personnel to trace the origin of an emergency (e.g., 911) telephone call, will not allow proper callback to the originating mobile subscriber.
On the other hand, waiting for all of the MSCs in the United States and perhaps Canada to be upgraded before implementing LNP would further delay the implementation of LNP in the largest 100 metropolitan service areas in the United States. It is generally recognized that both roaming and LNP are important aspects of wireless telephone service. Nevertheless, a plan has not yet been developed that will allow partial LNP implementation in the United States and Canada while maintaining roaming in those areas that are not LNP enabled.
Thus, there is a need for a method and system that will allow partial LNP implementation in the United States and Canada while maintaining roaming service in those areas that are not LNP enabled.